Abstract [en]

We studied crystal structures of potassium niobate (KNbO3) at high pressure by means of first-principles self-consistent total-energy calculations within the local density approximation using the full-potential linear muffin-tin orbital method. For the first time, we have calculated the atomic equilibrium volume, bulk modulus, total energy, and transition pressures for KNbO3, covering the full pressure range for which the above-mentioned experiments have been done. Two pressure-induced transitions are derived theoretically, namely one from orthorhombic (I) to cubic structure at around 13.2 GPa and a second from cubic to orthorhombic (II) structure at a pressure of 39.7 GPa. This fully confirms the recent experiments by Kobayashi et al (Kobayashi Y, Endo S, Ashida T, Ming L C and Kikegawa T 2000 Phys. Rev. 615819).